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Oxygen potential measurement of (U,Pu,Am)O$$_{2 pm x}$$ and (U,Pu,Am,Np)O$$_{2 pm x}$$

(U,Pu,Am)O$$_{2 pm x}$$及び(U,Pu,Am,Np)O$$_{2 pm x}$$の酸素ポテンシャル測定

廣岡 瞬; 松本 卓; 加藤 正人; 砂押 剛雄*; 宇野 弘樹*; 山田 忠久*

Hirooka, Shun; Matsumoto, Taku; Kato, Masato; Sunaoshi, Takeo*; Uno, Hiroki*; Yamada, Tadahisa*

(U$$_{0.623}$$Pu$$_{0.350}$$Am$$_{0.027}$$)O$$_{2}$$に対しては1,673, 1,773, 1,873K、(U$$_{0.553}$$Pu$$_{0.285}$$Am$$_{0.015}$$Np$$_{0.147}$$)O$$_{2}$$に対しては1,873, 1,973Kにおいて、酸素ポテンシャルの測定を実施した。測定は、熱天秤と酸素センサーを用いる気相平衡法により実施した。Uの代わりにAmを添加した場合、酸素ポテンシャルは大きく上昇した。同様に、Uの代わりにNpを添加した場合も酸素ポテンシャルは上昇したが、上昇の効果はPuやAmを添加した場合と比べても小さいものであった。酸素ポテンシャルの測定結果について、酸素分圧と定比組成からのずれをプロットし、欠陥化学により解析することで、欠陥反応の種類を推定した。推定した欠陥反応における平衡定数を評価し、AmとNpを平衡定数の中のエントロピーに組み込むことで、酸素ポテンシャルの測定結果を再現する評価式を導出した。

The measurement of oxygen potential was conducted at 1,673, 1,773, and 1,873 K for (U$$_{0.623}$$Pu$$_{0.350}$$Am$$_{0.027}$$)O$$_{2}$$ and at 1,873 and 1,923 K for (U$$_{0.553}$$Pu$$_{0.285}$$Am$$_{0.015}$$Np$$_{0.147}$$)O$$_{2}$$ by using a thermo-gravimeter and an oxygen sensor. Am inclusion in terms of substituting the U significantly increased the oxygen potential. Similarly, the inclusion of Np as a substitute for U increased the oxygen potential; however, the effect was not as large as that with the Pu or Am addition at the same rate. The results were analyzed via defect chemistry and certain defect formations were suggested in the reducing region and the near-stoichiometric region by plotting the relationship between PO$$_{2}$$ and the deviation from the stoichiometry. The equilibrium constants of the defect reactions were arranged to reproduce the experiment such that Am/Np contents were included in the entropy with coefficients fitting the experimental data.

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